Naltrexone is an effective narcotic antagonist. However, its effectiveness is limited by the need for high patient compliance, as oral dosages must be taken at least three times weekly. By using a proprietary delivery system, it is expected that naltrexone can be delivered at a controlled rate for one month. The delivery system to studied is biodegradable and biocompatible, and has been shown to cause no adverse tissue reactions in animal testing. It has been studied in vitro for the controlled release of several drugs and is currently being studied in humans under a Phase II IND. Most importantly, it can be injected using standard syringes and needles. Naltrexone will be incorporated into this delivery system. The effect of several variables including drug form and polymer composition, molecular weight and concentration, will be studied in order to obtain the desired release profile of 5 mg/day. The most promising formulation will be tested in rabbits for tissue compatibility.